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Showing posts from November 15, 2019

OSPF Interview Questions - Part 2

What are types of OSPF packets? Hello Database Description (DBD) Link-State Requests (LSR) Link-State Updates (LSU) Link-State Acknowledgements (LSAck) What is OSPF finite state machine? What are the states in OSPF neighborship? DOWN - No OSPF packets have been received on the interface ATTEMPT - Applies only to non-broadcast multi-access networks (NBMA) where the neighbors must be configured manually using the "neighbor x.x.x.x" command INIT - Router has seen a Hello message from an OSPF router TWO-WAY - A Hello message has been sent to the neighbor and the neighbor has replied with its Hello message. In Broadcast networks, the DR/BDR election takes place after this state EXSTART - DR and BDR establish OSPF adjacencies with each of the routers in the network. Master / Slave election takes place at this stage. The Master sends its DBD (Database Descriptor) first EXCHANGE - Routing information may be exchanged via DBD, Link State Requests (LSR) and Link State Updates (LS

OSPF Interview questions - Part 1

What is the protocol number of OSPF? 89 What is the multicast address of OSPF messages? for OSPF All-routers multicast for OSPF All-Designated routers multicast What are the OSPF hello packet timers? Hello packets are sent every 10 seconds with the Dead timer being 40 seconds Is it mandatory to have OSPF process ID the same on adjacent routers to form OSPF neighborship? No What is the impact of interface MTU mismatch on adjacent OSPF routers? MTU is not checked during the formation of neighbor adjacency. However, mismatched MTU values impede in the successful exchange of Database Description (DD) packets and thereby prevent the neighbors from reaching the "FULL" neighborship state. What are the types of OSPF LSAs? Type 1 - Router LSA Type 2 - Network LSA Type 3 - Summary LSA Type 4 - ASBR Summary LSA Type 5 - External LSA Type 6 - Multicast OSPF (MOSPF) LSA Type 7 - Not-So-Stubby-Area (NSSA)LSA Type 8 - External Attribute LSA for BGP Who generates Typ